1. Field of the Invention
The present invention relates to a method and device for measuring the rotational speed of a turbocompressor, in particular of a turbocharger of a motor vehicle. The invention is also directed to a motor vehicle that has such a device.
2. Description of Prior Art
Nowadays, many motor vehicles are provided with turbochargers that compress the intake air of the internal combustion engine. Such turbochargers run in the normal operating mode of the internal combustion engine without monitoring the rotational speed and/or other specific parameters such as the surge limit, flow separation, and damage to the charger. Owing to this lack of monitoring, malfunctions cannot be detected immediately.
First solutions for remedying this problem exist in that sensors are used that are based on magnetic operational principles (Hall, M R and the like). It is disadvantageous here that both the actual measuring (sensor element) and possible evaluation electronics have to be located in the “hot” region of the turbocharger, with the result that the corresponding components are subjected to high temperatures, which lead to measuring errors and reduce the service life of the components. Furthermore, to a certain extent pre-magnetized components are required, which constitutes a problem both in terms of the expenditure and the service life of the components. In addition, these magnetized parts act negatively as metal particle collectors.
Pressure sensors are used in conjunction with turbochargers to monitor the pressure generated by the turbocharger. For this purpose, piezo-resistive or capacitive sensors are usually used. The sensors are located in the air intake section of the internal combustion engine and measure the pressure of the air compressed by the charger. In order to achieve advantages determined during this pressure measurement in the areas of data processing and signal quality, signal filtering is used. The sensors are cut off, for example, by low pass filtering at approximately 2-10 kHz. Therefore, only signals below this limiting frequency are used for the pressure measurement.